A chemical amplification-type photosensitive composition is a pattern forming material capable of producing an acid in the exposed area upon irradiation with radiation such as far ultraviolet ray, and through a reaction using this acid as the catalyst, changing the solubility in a developer between the area irradiated with actinic rays and the non-irradiated area, thereby forming a pattern on a substrate.
In the case of using a KrF excimer laser as the exposure light source, a resin having small absorption in the region of 248 nm and having a basic skeleton of poly(hydroxystyrene) is predominantly used as the main component, and this is an excellent system capable of forming a good pattern with high sensitivity and high resolution compared to the conventional naphthoquinone-diazide/novolak resin system.
In the case where a light source of emitting light at a shorter wavelength, for example, an ArF excimer laser (193 nm), is used as the exposure light source, a satisfactory pattern cannot be formed even by the above-described chemical amplification system because the compound having an aromatic group substantially has large absorption in the region of 193 nm.
In order to solve this problem, a resist containing a resin having an alicyclic hydrocarbon structure has been developed as the resist for use with an ArF excimer laser. JP-A-2003-167347 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) (corresponding to US 2004/0058269 A1) and JP-A-2003-223001 describe a composition containing a resin having a polycyclic acid-decomposable repeating unit and a non-acid-decomposable repeating unit. This resin is a chemical amplification-type resist having a protective group which dissociates by the effect of an acid and is unstable to an acid, but amid increasing demands for a finer resist pattern, a sufficiently high resist performance can be hardly obtained only by such a protective group.
To meet such a requirement, a resist polymer where a crosslinked moiety capable of dissociating by the effect of an acid is introduced into the side chain of a resin containing a repeating unit having an acid-dissociatable protective group is also studied in JP-A-2000-214587 and JP-A-2001-106737 (corresponding to U.S. Pat. No. 6,403,281 B1). This is a technique of breaking the crosslinking bond by an acid catalyst and thereby enhancing the dissolution contract between the exposed region and the unexposed region. However, a bifunctional monomer such as diacrylate is used for the polymerization of the polymer and since a crosslinking reaction in the polymer side chain is involved, the polymer produced comes to have a very large molecular weight distribution and suffers from bad solubility. Moreover, an ultrahigh molecular weight polymer is readily produced and a sparingly soluble high-molecular-weight component which hardly dissolves in an alkali developer is present even after decomposition by the effect of an acid, as a result, there arises a problem that the undissolved component gives rise to a defect at the formation of a fine pattern.